The present invention relates to a melt spinning apparatus for producing nonwoven fabrics using a melt blowing technique and a melt spinning method by using the apparatus.
Melt blowing is a kind of a melt spinning method that involves extrusion of a molten feedstock resin into fibers to produce a nonwoven fabric. More specifically, a molten resin is extruded through a nozzle while receiving hot and high speed airflow directed toward the resin. This produces uncured resin filaments (threads). The filaments are fed onto a conveyor belt to form a sheet of a nonwoven fabric on the conveyor belt.
As a melt spinning apparatus for producing nonwoven fabrics using the melt blowing technique, an apparatus for producing transversely aligned webs is known as described in, for example, Japanese Laid-Open Patent Publication No. 2001-98455. The apparatus described in this document comprises a spinning nozzle for extruding a molten resin into a filament, an annular nozzle formed around the spinning nozzle to direct hot primary airflow to the filament extruded from the spinning nozzle, thereby applying vibration to the filament to stretch it, and a secondary airflow nozzle for directing hot secondary airflow to the filament at a position downstream from the annular nozzle.
The primary airflow flows downward while taking in the surrounding air, so it often experiences a drop in temperature. Thus, the primary airflow may cool the filament extruded from the spinning nozzle, which may be a cause of preventing the filament from being thinner. Taking this into consideration, the apparatus disclosed in Japanese Laid-Open Patent Publication No. 2001-98455 is intended to keep the high temperature of the filament with the secondary airflow directed to the filament after the primary airflow.
However, the apparatus disclosed in this document has the wall defining the secondary airflow nozzle at approximately right angles to the secondary airflow nozzle. Accordingly, the secondary airflow leaving the secondary airflow nozzle tends to experience an eddy turbulence. The eddy turbulence causes the filament to progress along a wavy path rather than a straight path. This makes it difficult to provide sufficiently thin filaments.